Although it is said that osmium oxides existing solely and firmly are oxides of osmium of 4 and 8 valences, but osmium oxides of 2, 3 and 6 valences can also exist.
An osmium oxide of 8 valences is usually called “osmium tetroxide”, or “osmic acid” in the case of an aqueous solution, and known as a superior oxidizing agent or catalyst in an organic synthetic reaction due to a great oxidizing ability thereof. On the other hand, however, it is also well known that osmium tetroxide is of high toxicity and sublimation character, having an offensive odor perceptible even at an extremely low concentration such as 2×10−5 mg/ml, and offending a mucous membrane of eyes or affecting adversely upon general respiratory organs with vapor thereof. Therefore, so far osmium tetroxide has been only used as an oxidizing agent for oxidizing a small amount of precious substance due to many problems in an industrial use thereof. In this connection, several attempts have been made to use osmium tetroxide safely for an industrial use.
For instance, a process for manufacturing catalysts based on nitrogen-containing polymers on which osmium oxide is precipitated from a solvent has been described in JP-A-4-505884, and actually a commercial product of about 1% by weight of osmium tetroxide carried on poly(4-vinylpyridine) (for instance, the one listed up in a catalogue of Sigma-Aldrich Corp.) is on the market.
However, it was not necessarily easy to produce an osmium tetroxide compound by said method, because said method always utilized a chemical bonding of an osmium oxide to a quaternary nitrogen atom, using a basic polymer having a nitrogen atom, in particular, a cross-linked polymer thereof. In addition, there was another problem that a polymer itself carrying said osmium oxide gradually decomposed when an osmium oxide compound obtained by said method was used as an oxidizing agent under an oxidative condition (Journal of Molecular Catalysis A: Chemical Vol. 120(1997), page 203 right column).
Furthermore, the osmium oxide in the osmium oxide compound disclosed in the above JP-A-4-505884 is not necessarily stably carried as osmium tetroxide, and is evidently inferior in a function as an oxidizing agent to that of osmium tetroxide itself, because it does not exist as osmium tetroxide, but as osmium trioxide or sometimes in a reduced state such as an oxide of a polymer or an oxo anion.
On the other hand, it has been lately reported that an optically active compound can be obtained by using an optically active ligand together with osmium tetroxide in a dihydroxylation reaction using osmium tetroxide in “Catalytic Asymmetric Snthesis” ed. by I. Ojima, VHC Publisher, New York, 1993, page 227–272; Chem. Rev., 94, 2483–2547(1994) and the like. However, it is difficult to recover and reuse osmium tetroxide from the viewpoint of safety in handling and the like because osmium tetroxide used in these asymmetric oxidation reactions is employed as it is, without being carried on a polymer or the like.
Furthermore, a polymer complex in which osmium tetroxide is coordinated with optically active ligands introduced into the polymer, and an asymmetric reaction using the above complex have been reported in Eur. J. Org. Chem., 1981, 21–27 and the like, but many problems are remaining unsolved in the production of such an osmium tetroxide compound, because it is not easy to produce a polymer itself in which an optically active ligand is introduced, and the polymer is necessary to be further reacted with osmium tetroxide. In addition, there is another problem that osmium tetroxide coordinated to the ligands gradually drops off during a reaction and cannot be reused.
Moreover, it has been attempted to make handling of an osmium oxide easy and improve solvent resistance thereof by microcapsulating said osmium oxide such as osmium tetroxide which is not easy to handle due to strong toxicity, using an olefin-based polymer such as polystyrene (JP-A-11-314038). Although this microcapsulated osmium tetroxide enabled use for an asymmetric dihydroxylation reaction due to an improved solvent resistance, it was used only for a reaction in a homogeneous solvent system, and in addition it was necessary to react a substrate gradually so as to strictly control the asymmetric reaction.
It is known that a heterogeneous asymmetric dihydroxylation reaction using potassium ferricyanide or the like as a co-oxidizing agent does not require a gradual addition of substrate to the reaction system, and therefore gives a high optical yield in a short reaction time, while an asymmetric dihydroxylation reaction in a homogeneous solvent system generally requires a gradual addition of substrate to the reaction system so as to obtain a high optical yield.
Thus, it has been desired to create a new compound to carry osmium oxide as an oxidizing agent that enables an asymmetric dihydroxylation reaction in a heterogeneous solvent system where a conventional operation or the like to control an asymmetric reaction is not required.